With the improvement of scientific and technological level, the consumer electronics enter people's lives at a rapid pace, and head-mounted display products attract the attention of people by virtue of the gorgeous appearances and the advanced functions. Head-mounted display products apply visual technology perfectly to display images with an LCD screen of a high resolution, and amplify the images with a lens so that the user can view clear images. In addition, the images are processed with 3D technology so that the user feels a visual impact from 3D technology. However, the images are distorted while being amplified by the lens. The distortion is a geometric distortion of imaging, and is a screen twisted deformation phenomenon caused by the different magnification powers to an image in different areas of the focal plane. The degree of the deformation progressively increases from the screen center to the screen edges, and is mainly obvious at the screen edges. Thus the distortion amount should be measured to recover the distorted image into the normal image through image processing technology. Methods for measuring lens distortion in the prior art have slow calculation speeds and low measurement accuracies, and a large error will be caused after the recovering into the normal image, which cannot satisfy requirement on image processing.